1. Field of the Invention
The present invention relates to a distillation column assembly combining two distillation columns used in a distillation process.
2. Discussion of Related Art
A variety of raw materials such as crude oil are usually composed of a mixture of many compounds. These raw materials are rarely used by themselves industrially, but are usually used after being separated into respective compounds. A representative chemical process for separating the mixtures is a distillation process.
The distillation process typically involves dividing the mixture into two components: a high boiling-point component and a low boiling-point component, and thus uses distillation columns of a number (n−1) that is one less than the number (n) of components of a mixture to be separated. That is, to separate a three-component mixture in the typical distillation industrial field, at least two distillation columns must be used. Most practical processes also use a serial structure of two distillation columns.
The typical distillation process of separating the three-component mixture is as shown in FIG. 1.
This process is a dual column method of separating a lowest boiling-point component D in a first column 11 and separating an intermediate boiling-point component S and a high boiling-point component B in a second column 21. In such a method, a phenomenon in which the intermediate boiling-point component S is again mixed at a lower zone of the first column generally occurs.
The process of separating the three-component mixture using two serial columns is disclosed in Korean Patent Application Publication No. 10-2003-0088211 (KR 10-2003-0088211), which was published on Nov. 19, 2003, by way of example. This patent document discloses a method of operating two distillation columns to refine normal butanol. The related art can refer to this method, and the disclosure of KR 10-2003-0088211 is incorporated by reference herein in its entirety.
In the aforementioned process, while the composition of a product can be easily controlled, a remixing process of the intermediate boiling-point material takes place in the first distillation column. This acts as a main factor of reducing thermodynamic efficiency in the distillation column, thus resulting in additional unnecessary consumption of energy.
To improve limitations of this distillation column, there has been a proposal for a dividing wall column (DWC). The DWC has a structure in which a preliminary separator is integrated with a main separator in a main column by installing a dividing wall in the main column. The DWC having this structure has a great advantage in that two distillation columns are integrated into one distillation column, so that investment expenses can be remarkably saved. That is, since the two distillation columns are integrated into one distillation column using the dividing wall, the DWC fundamentally eliminates a problem of reduction in energy efficiency due to remixing of the intermediate boiling-point component which occurs when two typical distillation columns are used. In general, the DWC has been known to have an energy saving effect of about 30% (maximum 60%) and an investment expense saving effect of 20% to 30% in comparison with the typical distillation column. Since the DWC requires a small space and has a high effect of improving yield/purity, the DWC is frequently applied to new distillation columns as well as for revamping existing distillation columns. The DWC can be applied to separation of any three or more component systems if a separation pressure difference and a utility temperature difference are not very great. As such, the DWC has very wide technical applications.
Particularly, the DWC shows excellent improvement in performance under the following conditions: (1) when there is relatively much of the intermediate boiling-point component, (2) when high-purity separation of the intermediate boiling-point component is required, and (3) when product standard and relative volatility distributions are uniform. An internal structure design for a dividing wall section for separating main and preliminary distillation parts, prediction of heat transfer characteristics and the height equivalent to a theoretical plate (HETP) in the dividing wall section, computer simulation technology for predicting separation characteristics, securing of operation and control performance, etc. are important technical issues.
The distillation process requires 19% of the total consumption of energy of Korean industries and 11% of the total consumption of national energy. This is a tremendous amount corresponding to 16,700,000 TOE of the amount of energy used and 14,600,000 TC (based on heavy oil) of the amount of CO2 emission. Petrochemical industries require 24% of the amount of total consumption of Korean national energy (16.4×107 TOE based on 2003). 50% of the total consumption of energy of the petrochemical industries is caused by a separating process, and 85% of the total consumption of energy of the separating process is caused by a distillation process.
The distillation process is such a representative energy-intensive process as to require 5.4% of the total consumption of national energy in the case of the United States and 13% of the total consumption of national energy in the case of the United Kingdom.
Energy expense in the petrochemical industries amounts to about 7% over the sales and greatly exceeds a range of 2% to 4% that is a mean profit rate of the corresponding industries, thus becoming a considerable burden on business administration. Further, countries worldwide have signed the Framework Convention on Climate Change, and carbon emission rights of each country have become an issue. Therefore, a problem with energy expense saving is directly associated with a problem with reduction in CO2 emission.
In this situation, the necessity to develop energy-saving technology in the distillation process is very high. Despite the urgent need to save energy, the introduction of a new process is very difficult due to high facility investment expenses, compared to other fields. That is, since the distillation process is a process industry whose facility expenses are very high, it is difficult to derive economic feasibility to introduce the distillation process even when a new energy-saving apparatus is developed. In this respect, the best measure is merely to optimize a method of operating a previously installed apparatus in the related art.
For this reason, it is very urgent to develop an energy-saving distillation apparatus capable of readily, economically replacing an existing apparatus.
As described above, the DWC has a comparative advantage in terms of the energy-saving effect and the facility investment-saving effect compared to existing typical distillation columns. Thus, it is possible to obtain a desired energy-saving effect by replacing the existing typical distillation column with the DWC.
However, even when the separating processes for all kinds of chemicals are simply replaced with the DWC, energy is not actually saved. Particularly, when the separation pressure difference and the utility temperature difference are great, the energy-saving effect of the DWC may be extremely slight, or an adverse effect may actually occur.
In summary, the energy-saving distillation apparatus capable of replacing the existing distillation apparatus has to meet the following requirements: (1) a high energy-saving effect, (2) a possibility of economically replacing the existing process without a great change, (3) applicability even when the separation pressure difference and the utility temperature difference are great, and so on.